Machines, such as construction machines (e.g., tractors, dozers, loaders, earth movers, or other such pieces of equipment), may have any number of structural components that are subject to fatigue damage which could lead to structural failures. One method for monitoring fatigue damage on a machine structure is to perform a manual, direct visual inspection to look for actual fatigue damage. However, such a method may be impractical for several reasons. First, such an inspection may not be as comprehensive as desired. This may be due, in part, to the difficulty of accessing some components of the machine, such as when the structure in question is concealed and cannot be viewed without dismantling a portion of the machine. Second, a manual inspection of structural components can only be performed on a periodic basis, yet fatigue damage and resulting catastrophic failure still can occur between inspections. Third, a manual, direct inspection may detect fatigue damage that is manifest by observable cracks, but it may not be able to detect fatigue damage before cracks occur, or predict the remaining fatigue life. While manual inspection may provide some insight into damage that is visible to an inspector, (e.g., large visible cracks in a machine component), internal damage may not be readily apparent through manual inspection (e.g., small internal cracks in a component).
Some systems have been proposed utilizing various ways of monitoring structures electronically to detect fatigue damage. For example, some systems include strain gauges mounted on an exterior surface of a structural component. However, such a mounting location often positions the strain gauges offset from the neutral axis of the structural member, which may result in errors in measuring strain due to bending in the structural component rather than strain (e.g., shear, elongation, torsion). In addition, some machines have structural components that are used in harsh environments. For example, a forestry machine may be operated amongst trees and bushes with branches that can damage externally mounted gauges and related equipment. Systems have been developed that utilize wireless strain sensing devices. However, wirelessly transmitting high volumes of data that result from rapid sampling may not always be practical or possible. In addition, supplying power to such wireless strain sensing devices may also present a challenge.
Other systems have been developed that include internally mounted strain sensing devices. For example, U.S. Pat. No. 6,858,809 to Bender (“the '809 paten”) discloses a system including internally mounted strain sensing devices that are configured to take strain measurements. The system of the '809 patent includes a strain sensing element mounted directly to the inner surface of a bore within a hinge pin.
While the system of the '809 patent may provide an internally mounted strain sensing element, mounting of such elements directly to the inner bore can be difficult. The '809 patent offers little detail regarding the structure of such strain sensing devices and little information about how to mount such devices. Retrofitting such devices may present significant challenges, particularly for machines that are not located at or near a facility at which the installation may be performed and/or for machines that are not readily movable to such locations.
The present disclosure is directed to improvements in fatigue evaluation systems.